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Saturday, March 15, 2014

Can penguins cope with climate change? Scientists find different types of ice elicit different responses

mongabay.comMarch 13, 2014

Pygoscelis adeliae).
In an article recently published in PLOS ONE, a team of researchers led
by Amélie Lescroël from the Centre d'Ecologie Fonctionnelle et
Evolutive (CNRS) in France, found that changes in sea-ice content and
newly formed icebergs significantly impacted Adélie penguin communities
in the Ross Sea.

Climate change is leading to major shifts in sea ice. One of the largest
glaciers in Antarctica has begun to melt at a rate some scientists
describe as irreversible. Pine Island Glacier contributes a fourth of
the discharge of the West Antarctic Ice Sheet. It is estimated that if
this entire ice sheet were to melt, sea levels would rise by ten feet.
Other areas of the Antarctic are experiencing cooling events, resulting
in greater ice coverage known as "fast ice." However, scientists
believe that melting will supplant fast ice in the near future.

"While net sea ice cover (i.e., the area of ocean covered by ice) has
increased over the past few decades [in Antarctica] owing to wind
changes brought largely by mid-latitude warming and the Antarctic Ozone
Hole, modeled predictions point to a decrease by 5-15 percent, depending
on sector, by 2025-2052," the study states. "Concomitantly, increased
ice shelf instability will lead to more frequent iceberg calving,
including very large icebergs (hundreds of square kilometers)."

Sea ice cover variability directly affects Adélie habitat, and the
species' ability to adjust to this variability will determine their
future.

Adélie penguins depend on sea-ice for foraging, resting, molting,
breeding and migrating. They are one of only two penguin species that
depend on sea ice and not icebergs, the other being the Emperor penguin (Aptenodytes forsteri).

"This 'dependence' is actually a manifestation of them being the only
penguin species that are able to cope with sea ice," Lescroël told
mongabay.com.

To a certain extent, Adélie penguins are adapted to cope with changes in
their habitat. For instance, they're able to easily gain and lose fat
depending on ice conditions, and dive for longer periods of time
compared to other penguin species.

"They dive mostly between 10 and 50 meters deep to catch their prey but
can dive up to 180 meters, which is a world record," said Lescroël.

The southernmost extent of Adélie habitat is the Ross Sea, where 38
percent of the world's population resides. Lescroël and her colleagues
evaluated data that had been collected over thirteen years at Cape
Crozier on Ross Island, a volcanic island located near the Antarctic
mainland.

The researchers conducted their study in a fenced-in nesting area
installed in 1996, allowing penguins access through only one entrance
outfitted with a scale. They collected each penguin's trip duration as
well as changes in weight within breeding seasons and over multiple
years. Using these data, the researchers were able to record how long it
took the penguins to forage and how much food they brought back to
their chicks.

"When they are nesting, parents take turns on the eggs or chicks,"
Lescroël said. "One of the parents stays at the nest while the other
goes [to] sea to catch food. On Ross Island, Adélie penguins feed on
crystal krill and silverfish. They swallow the prey as they catch it,
underwater. When they come back to the nest, they regurgitate the food
to their chicks."

Since Adélie penguins depend on sea-ice, one might expect the increased
presence of "fast ice" in some areas would equate to habitat expansion.
However, the study's findings indicate this is not necessarily so. When
there was less sea-ice, the penguins were able to fish for longer
periods of time and bring more food back to their chicks.

"This is mainly because when there is lots of concentrated sea ice,
penguins have to walk over the sea ice (rather than swim) to reach the
open water where they could dive," Lescroël said. "This is more costly
in time and energy. But this is when environmental conditions are
"normal."

In the middle of the study, when four giant icebergs broke off as a
result of increased melting the research team labeled this as an extreme
environmental event. The icebergs were present in Cape Crozier's
landscape for 5 years, and the unique event allowed the team to observe
how Adélie penguins responded to icebergs.

"The presence of these icebergs dramatically changed the physical
environment of the penguins in many ways: less open water was available
for diving; penguins were disoriented due to the movements of these huge
blocks of ice just in front of the colony; there was less ocean
productivity in the first year; and there were changes in the drift
pattern of pack ice," Lescroël said, adding that "the changes were so
extreme that sea ice concentration did not matter anymore. The foraging
efficiency of Adélie penguins was constrained to lower levels during
these five years, no matter what the sea ice concentration was."

While the icebergs were present, fewer chicks were reared than usual
although the number of adults was not affected. However, soon after the
icebergs left the area, breeding levels returned to normal.

"Our work shows that if the frequency of such extreme events increases,
then it will become very hard to predict how penguin populations will
buffer future sea ice changes," Lescroël said.

Map
of the study area provided in the PLoS ONE article. The colony location
is indicated by the star, the foraging area of Adelie penguins (in red)
and where the giant icebergs were located. Satellite images are from
http://lance-modis.osdis.nasa.gov. A: Illustrates a typical iceberg year
(Dec. 21, 2004). B: Illustrates a typical non-iceberg year (Dec. 21,
2008).